Integrating Advanced Computer-Aided Design,


and Numerical Control: Principles and Implementations

Xun Xu University of Auckland,

New Zealand

Information Science reference Hershey • New York

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Library of Congress Cataloging-in-Publication Data Xu,

and numerical control : principles and implementations / by Xun Xu

Includes bibliographical references and index

Summary: “This book presents basic principles of geometric modelling while featuring contemporary industrial case studies”--Provided by publisher

ISBN 978-1-59904-714-0 (hardcover)


Industrial--Data processing

Geometrical models--Data processing

CAD/CAM systems

X86 2009 670

All work contributed to this book is new,

previously-unpublished material

The views expressed in this book are those of the authors,

but not necessarily of the publisher

If a library purchased a print copy of this publication,

com/agreement for information on activating the library's complimentary electronic access to this publication

Dedication To my wife Wei Cui,

my daughters Sylvia and Cecilia,

and to our parents Zuxing Xu and Huaizhen Zhou,

Table of Contents


Section I: Principles and Backgrounds Chapter I Geometric Modelling and Computer-Aided Design

Data Interoperability

Volumetric Features


Principles of Numerical Control


Organization of Offsets

Geometry Offsets

Section II: Integration and Implementations Chapter X Integration of CAD/CAPP/CAM/CNC


CAM and CNC Systems

Adptable CNC System

Method-Level Data

Chapter XIV Integrating CAD/CAPP/CAM/CNC with Inspections

PLM and Beyond

PLM Solution Model


The late Dr

Eugene Merchant,

then director of research planning of Cincinnati Milacron Inc

made an interesting Delphi-type technological forecast of the future of production engineering at the General Assembly of CIRP in 1971

Five years later,

he made another report on the “Future Trends in Manufacturing – Towards the Year 2000” at the 1976 CIRP GA

He reported that between now (1976) and the then (2000),

the overall future trend in manufacturing will be towards the implementation of the computer-integrated automatic factories

More than 30 years have since whisked past,

manufacturing technology had progressed even faster than Dr

Merchant’s prediction

One of the forerunners of automated manufacturing is the CAD/CAM technology which had made its debut more than 30 years ago

Numerous research papers and books have since been written on the topic

As new technologies constantly emerge and efficient IT tools,

and faster and affordable computing facilities become more pervasive,

the demand for updating the development of this field is clear

The author of this book has put together a comprehensive perspective of computer-aided design,

manufacturing and numerical control,

addressing their retrospective developments,

present state-of-the-art review and future trends and directions


underpins all manufacturing activities at an early stage of a product development process

The design stage is well known to have the capability of locking in most of the subsequent costs,

and any changes made will prove to be unwise and expensive

Concurrent engineering has provided a solution to this problem to some extent,

The intricacy and interactions of all the related activities,

ecological aspects of manufacturing,

would need to be thoroughly understood

This book has elucidated many connected aspects of automated manufacturing such as CAD,


evolutionary computing techniques,

In particular,

the theoretical and practical aspects of these technologies,

which may be integrated effectively,

It provides an invaluable updated text and reference for senior students,

I am delighted that the author has generously shared years of his own research expertise,

as well as those of the others with such a fine effort

I congratulate the author on having produced this splendid new book

PhD National University of Singapore Fellow of Institution of Engineers,

Singapore Fellow of Society of Manufacturing Engineers (SME),

USA Fellow of International Academy for Production Engineering Research (CIRP) Regional Editor for International Journal of Advanced Manufacturing Technology Regional Editor for International Journal of Machine Tools and Manufacture Associate Editor for Journal of Manufacturing Systems Associate Editor for Journal of Manufacturing Processes

Nee is a professor of manufacturing engineering,

Department of Mechanical Engineering,

National University of Singapore (NUS) since 1989

He received his PhD and DEng from Manchester and UMIST respectively

His research interest is in computer applications to tool,

distributed manufacturing systems,

virtual and augmented reality applications in manufacturing

He is a Fellow of CIRP and a fellow of the Society of Manufacturing Engineers (USA),

He had held appointments as head of the Department of Mechanical Engineering,

Dean of Faculty of Engineering,

co-director of Singapore-MIT Alliance (SMA),

he is the director of Research Administration of NUS

He has over 200 refereed journal publications and 8 authored and edited books


he is regional editor of the International Journal of Advanced Manufacturing Technology and the International Journal of Machine Tools and Manufacture

He is also editorial board member of some 20 refereed journals in the areas of manufacturing and precision engineering

Preface Since the very first computer (Electronic Numerical Integrator And Computer,

ENIAC for short) was conceived,

and built in 1946 at the University of Pennsylvania’s Moore School of Electrical Engineering,

its impact on almost all walks of our lives has been readily recognisable

Computers have certainly been responsible for the modern manufacturing industry that exists today


applications of computers have been found in the entire spectrum of the product development process,

ranging from conceptual design to product realization and even recycling


every manufacturing organization needs a well thought-out,

long-term strategy in investing computer-related technologies,

Selecting vendors and defining the scope of each business system from a plethora of rapidly changing options is incredibly difficult

Claims and testimonials are hard to evaluate against your business requirements

Previous generations of computer-based systems have had clean boundaries between system types as well as data formats,

such as computer-aided design,

process planning and manufacturing (CAD/CAPP/CAM),

computer numerical control (CNC),

product data management (PDM),

and product lifecycle management (PLM) systems

whereas boundaries between today’s products and product development processes are fuzzy

Some vendors offer a full suite of products covering “all” needs,

while others focus on a specific business need and provide a “best-of-breed” system,

leaving it to customers to debate the benefits of each

Most users,

even those choosing a product suite,

will need to interface or integrate with multiple systems

Each organization and the systems to be interfaced and integrated have unique requirements and necessitate comparing those needs to the organization’s long-term interconnection strategy

COMPUTER AIDED TECHNOLOGIES One of the areas that computers were first used to assist in engineering process is design,

hence the birth of computer-aided design technology

Three-dimensional (3-D) computeraided design models led to the development of new branches of technologies such as computational graphics and geometric modelling

These technologies are needed to serve as the underlying principles for a complete and unambiguous internal representation of any product

The wire-frame and surface-based models were first developed

A need for solid modelling then arose with the development of application programs such as numerical control (NC) verification codes and automatic mesh generation for finite element analysis (FEA)

The research work on solid modelling technology commenced in the mid-1970s,

and a decade later the technology was seen to be utilized by a number of CAD systems that are advanced enough to represent most of the common geometric entities,

thanks to the underpinning solid modelling kernels such as ACIS®,


Most of these systems use a boundary representation (B-rep) scheme to represent 3-D information

It is also noticeable that computer hardware advancements have been in company with the development of geometric modelling techniques and CAD systems

The hierarchy of CAD hardware resources has progressed from large-scale computers to workstations and PCs

This trend was not accompanied by a reduction in functionality,

owing to the rapid advancement of computer hardware

Two critical advancements in the domain of computer-aided design are parametric and feature-based design (FBD) technology

Parametric design is a method of linking dimensions and variables to geometry in such a way that when the values change,

the part changes as well – hence the dimension-driven capability

Designing with pre-defined features can reduce the number of input commands substantially

The most valuable attribute however,

is the fact that the features can be used to capture the designer’s intent as well as to convey other engineering connotations

These days,

users can easily be “spoiled” by a large number of choices of CAD systems offering targeted competitive solutions

While this may not be a bad thing,

has proven to be more than a nuisance

Companies are more and more involved in manufacturing various parts of their end-products using different subcontractors,

many of whom are often geographically diverse as well as operationally heterogeneous

The rise of such globalization has created an acute need for sharing and exchanging information among vendors involved in multi-disciplinary projects

Accurate data transmission is of paramount importance

a mechanism for good data transfer is needed

Direct data translators provide a direct solution,

which entails translating the modelling data stored in a product database directly from one CAD system format to another,

A more viable option however,

is the use of a common translator,

which converts a proprietary CAD data format into a neutral data format and vice versa

This neutral data format may be of an international or industry accepted data format or a proprietary data format

Among these standards is STEP (Standard for the Exchange of Product model data),

the only international standard that is soon becoming the norm of product data exchange

Representation of a product’s geometry and topology is just the beginning of any product development process

Manufacturing is often one of many subsequent activities

When computers are used to assist process planning and manufacturing activities (i

CAPP and CAM),

multiple benefits can be derived

CAPP relies on the produce model data provided by a CAD system to perform precise and consistent process planning for manufacturing

The key research issue herein stems from the differing product descriptions used,

CAD is usually geometry-based whereas CAPP is manufacture-oriented (Zhou,

Wang & Ruan,

It is a common practice to use design features in a CAD model and manufacturing features in a CAPP and/or CAM system

Design features are stereotypical shapes related to a part’s function,

or the model construction methodology,

whereas manufacturing features are stereotypical shapes that can be made by typical manufacturing operations (Shen & Shah,

A feature,

be it a design feature or a manufacturing feature,

can be represented as a collection of faces or a solid

Careful examination about which representation scheme suits the jobs of process planning and manufacturing best,

suggests that the volumetric scheme has more advantages over the surface scheme (Xu,

The differences between design features and machining features,

and the need for “deriving” one from the other,

have led to a new field of research: feature recognition


the goal is to bridge the gap between a CAD database and a CAPP system by automatically recognizing features of a part from the data stored in the CAD system

Based on the recognized features,

then one has to drive the CAPP system which produces process plans for manufacturing the part

It is important to acknowledge that the task of recognizing manufacturing features still remains with the usage of a feature-based design (FBD) tool

The reason is obvious

design features would be used in a FBD system and manufacturing features are needed for process planning

Difficulties in developing a generic feature recognition system arise from both presentational challenges of specifying the analysis required,

and from computational challenges (Corney,

Sundararajan & Wright,

When features come to interact with one another,

recognizing and interpreting them can be even more difficult

Feature interactions tend to violate feature validity one way or another,

which in turn may affect the semantics of a feature,

ranging from slight changes in actual parameter values,

to some substantial alterations to both geometry and topology,

or even complete suppression of its contribution to the model shape

More importantly,

feature interactions also impact on process planning and manufacturing

Let there be no doubt that features are a common thread in any CAD,

They are often used to interface or integrate CAD,


confusion often exists between integrated and interfaced feature technologies

One difference between interfacing and integration is that interfacing can be achieved at the result level,

while integration must be addressed at the task level

In order to achieve an integrated environment and to make sure the features formed can be directly related to machining processes,

machining information needs to be considered,

such as roughing and finishing operations,

as well as the cutting tools that may be used

In a feature-based design system,

feature mapping from design to manufacturing can be an option

The process plan for a part is usually further processed in a CAM system/module to obtain a set of machine control data (MCD),

which is then used to drive a CNC machine tool

Numerical controllers were developed in the late 1940s and early 1950s by John T

Parsons in collaboration with the MIT Servomechanisms Laboratory

The first CNC systems still used NC-style hardware where the computer was used for the tool compensation calculations and sometimes for editing

Today’s CNC machines have advanced to a point of little resemblance to their predecessors

With the increased automation of manufacturing processes using CNC machining,

considerable improvements in consistency and quality have been achieved

The MCD codes (or G-codes) used on a CNC machine contain mostly sequential machining commands that are structured in blocks of data

An alternative to G-codes when it comes to manually programming a CNC machine is the Automatic Programming Tool (APT)

APT can describe some simple parts without using a 3-D modelling system or a graphics user interface

For complicated parts however,

one has to use some of the contemporary tools (e

CAD/CAM systems)

These systems can work with a design model,

which is augmented with manufacturing information such as machining features and machining parameters,

In the recent past,

manufacturing companies have been facing increasingly frequent and unpredictable market changes

As such,

there is a recognised need for CNC machine tools to be further advanced so that they become more open,

Issues related to both hardware and software need more

More research seems to have been directed toward software improvement rather than hardware improvement

A noticeable advancement has been the development,

and implementations of a new international standard for CNC data models,

STEP AP238 or ISO 14649,

both collectively known as STEP-NC)

Unlike G-codes,

STEP-NC contains higher-level information such as machining features


and CNC are by and large localized within each of their domains,

forming so-called individual “automation islands”

Though there has been some success in bringing CAD,

there has been a lack of a universal platform on which data conversion across the board can be kept to a minimum

In fact,

the gap between CAD/CAPP/CAM and CNC is even larger

The STEP standard was initially designed to offer a neutral data exchange method in replacement of IGES


the standard is much more than a neutral data format that translates geometrical data between CAD systems

The ultimate goal of STEP is to provide a complete computer-interpretable product data format,

so that users can integrate business and technical data to support the whole product life cycle: design,


most of the commercial CAD systems can output STEP AP203 and/or STEP AP214 files via STEP translators

By implementing STEP AP203 and STEP AP214 within CAD systems,

data exchange barriers are only partially upheaved in a heterogeneous design environment

This is because both APs only document pure geometric information,

leaving high-level data such as features behind


data exchange problems between CAD/CAPP/CAM and CNC systems still remain unsolved

This is because on the output side of a CAM system,

the 50-year-old international standard ISO 6983 (i

G-code) still dominates the control systems of most CNC machines


ISO 6983 has become an impediment for the contemporary collaborative manufacturing environment (Xu & He,

In order to achieve a complete integration of CAD,

a suite of STEP Application Protocols may be used

When STEP AP224 is used to bridge CAD with CAPP,

information more than just geometry and topology can be shared

This information includes machining feature information

dimensional and geometric tolerances

material properties and process properties

and even administrative information

STEP AP240 can support macro process planning by connecting CAPP with CAM

This is because AP240 defines such a high-level process plan for a machined part,

and contains data about manufacture of a single piece or assembly of single piece parts

It serves as an interface for capturing technical data out of the upstream application protocols,

and issuing work instructions for the tasks required to manufacture a part and the information required to support NC programming of processes specified in the process plan

After macro process planning comes the micro process planning,

which acts as a link between CAM and CNC

This can be done via STEP-NC

STEP-NC defines the process information for a specific class of machine tools

It describes the task of removing volumes defined as AP224 machining features in a sequential order,

and with tools that meet all engineering and design requirements

In essence,

STEP-NC describes “tasks”,

while G-code describes “methods” for CNC machines

The task-based NC programs can be made portable across different machine tools

Modifications at the shop-floor can

also be saved and transferred back to the planning department that enables a better exchange and preservation of experience and knowledge

Different STEP Data Access Interfaces (SDAI) may be used for implementing a STEPcompliant environment

Thus integrated product data can be easily managed by making complex engineering applications available across data implementations

Use of STEP-NC in replacement of G-code also promises a new generation of CNCs that are open,

Alongside STEP-NC,

the function block technology offers a complementary solution

Function blocks are based on an explicit event driven model and can provide for data flow and finite state automata-based control

Based on previous research,

function blocks can be used as the enabler to encapsulate process plans,

integrate with a third-party dynamic scheduling system,

monitor process plans during execution,

and control machining jobs under normal and abnormal conditions

They are suitable for machine-level monitoring,

shop-floor execution control and CNC control (Wang & Shen,


since the business of product development and manufacturing goes beyond activities such as design,

Extension of an integrated CAD/CAPP/CAM/CNC system may occur in both vertical and horizontal dimensions

Vertical integration may be backward or forward in the spectrum of a product development process

An example of forward vertical integration can be inspection as it is a logic step after CNC machining

With inspections,

Closed-Loop Machining (CLM) can be realized to maximize the efficiency of a machining process by exercizing a tight control in a manufacturing system

Probing is defined in STEP-NC for inspection operations,

and the dimensional inspection data model is specified in ISO 10303 AP219

it has become possible to consolidate machining and inspection operations in one single program


businesses have increasingly moved to outsourcing many functions,

leading to the need for horizontal integration

Companies that have been practicing CAD/CAPP/ CAM/CNC integration have now realized that there is a need to operate in a much broader scope with wider boundaries

This leads to the increased implementation of PDM and PLM systems

PDM systems integrate and manage all applications,

and processes that define a product,

PLM brings PDM into an even broader paradigm in that all the information pertaining to the lifecycle of a product is actively managed

Unlike PDM,

PLM is much more than a technology or software product

PLM is a strategic business approach that empowers the business

Extensions of CAD/CAPP/CAM/CNC integration,

have a common request for an environment in which manufacturing businesses should operate

companies often have operations distributed around the world,

and production facilities and designers are often in different locations

Such globalization means that companies should be able to design anywhere,

and maintain anywhere at any time

Manufacturing engineers need to employ collaborative tools during planning to help improve production processes,

and to allow earlier impact on product designs

For all of this to happen in an orderly manner,

STEP and XML combined with the latest multi-tiered network technology can provide such a solution

EMBRACING THE TECHNOLOGIES While computers have proven to be instrumental in the advancement of modern product design and manufacturing processes,

the role that various technologies have played can never be over-estimated

In the recent years,

there has been a wealth of technologies being used in CAD/CAPP/CAM/CNC

Among them are the knowledge-based (expert) system,

Petri Nets,

An expert system is a computer system that has a well-organized body of knowledge in a bounded domain,

and is able to simulate the problem solving skill of a human expert in a particular field

Artificial neural networks,

are techniques that simulate the human neuron function,

using the weights distributed among their neurons to perform implicit inference

Neural networks have been used to assist both automatic feature recognition and process planning

Genetic algorithms mimic the process of natural evolution by combining the survival of the fittest among solution structures with a structured,

The agent-based technology utilizes agents as intelligent entities capable of independently regulating,

reasoning and decision-making to carry out actions and to achieve a specific goal or a set of goals

Agent-based approaches enable functionality for distributed product design and manufacturing (i

upgradeability and robustness)

Other technologies such as fuzzy logic,

Petri Nets,

and ant colony optimisation methods have also been used

There is,

a consensus that systems developed using a combination of two or more such technologies fare better than otherwise

ORGANIZATION OF THE BOOK The book is organized into two sections and altogether 17 chapters

Section I,

titled “Principles and Backgrounds”,

named “Integration and Implementations”,

A brief description of each of the chapters follows: Chapter I,

“Geometric Modelling and Computer-Aided Design” reviews various geometric modelling approaches,

and solid modelling techniques

Basic computational geometric methods for defining simple entities such as curves,

Concepts of parametric,

variational and feature-based design in a CAD system are explained

Chapter II “CAD Data Exchange and CAD Standards” discusses the data interoperability issues,

such as the different types of data translation and conversion methods

The common data exchange protocols are explained together with some examples

These data exchange protocols include DXF,

Chapter III,

“Computer-Aided Process PLannning and Manufacturing” presents the basic concepts of,

a computer-aided process planning and manufacturing

Two principal approaches of CAPP are discussed

They are manual experience-based planning method and computer-aided process method

Chapter IV,

“Feature Technology” gives an overall view of feature technology

Features are defined and classified according to design and manufacturing applications

Issues about surface and volume features are discussed and different feature-based methodologies are presented

Chapter V,

“Feature Recognition” discusses some of the basic issues and methodologies concerning feature recognition

Feature recognition systems are divided into two different types: feature detection and feature generation

Issues regarding concavity and convexity of a geometric entity,

optimal interpretation of machineable volumes and the necessity of considering raw workpieces are all discussed at a length

Chapter VI,

“Feature Interactions” analyses the feature-feature interaction problems,

which have a strong bearing on process planning

Feature interactions may be studied on the basis of surface information and volumetric information of a part

Either way,

identification of interacting entities is the key to an effective way of dealing with feature interactions

Chapter VII,

“Integrated Feature Technology” addresses feature technologies from the integration point of view

When features are recognized,

the related machining operations and cutting tools are considered

For a feature-based system,

mapping design features to machining features can be an effective method

Chapter VIII,

“CNC Machine Tools” presents an overview of CNC machine tools and their designations of axis and motion

The tooling for CNC machine tools is also discussed

Chapter IX,

“Program CNCs” provides a detailed account of the basics of CNC programming

The emphasis is on the G-codes and APT

To programme using G-codes,

both compensation and interpolation are the key issues

Chapter X,

“Integration of CAD/CAPP/CAM/CNC” begins with a general description of traditional CAD/CAPP/CAM/CNC integration models

This is followed by an industry case study showcasing how a proprietary CAD/CAM system can be used to achieve centralized integration

Chapter XI,

“Integration Based on STEP Standards” presents a scenario whereby CAD,

The underlying mechanisms are those enabled by the STEP standard,

or rather its suite of Application Protocols

Function blocks also contribute to building such an integrated environment

Chapter XII,

“Function Block-Enabled Integration” introduces the function block architecture that has been implemented in two types of integration

The first brings together CAD,

and CAM and the second connects CAM with CNC

Chapter XIII,

“Development of An Integrated,

Adaptable CNC System” discusses topics related to the task-level and method-level information in machine control data,

and the methodology of converting the task-level data to the method-level data

Chapter XIV,

“Integrating CAD/CAPP/CAM/CNC with Inspections” discusses the extension of CAD,

and CNC to include inspections

The objective is to maximize the efficiency of a machining process by maintaining a tight control in a manufacturing system

Chapter XV,

“Internet-Based Integration” describes the methods of developing an Internet-enabled,

and CNC system to support collaborative product development

The main goal is to provide a team environment enabling a group of designers and engineers to collaboratively develop a product in real time

Chapter XVI,


and Beyond” presents an even broader scope and wider boundary in which CAD,

and CNC systems need to operate,

PDM and PLM)

PDM systems integrate and manage all applications,

PLM brings PDM into an even broader scope in that all the information pertaining to the lifecycle of a product is actively managed

Chapter XVII,

“Key Enabling Technologies” discusses some key enabling technologies in the field of design and manufacturing

These are knowledge-based systems,

Also briefly mentioned are the fuzzy logic,

Petri Nets,

and ant colony optimisation methods

WHO AND HOW TO READ THIS BOOK This book has three groups of people as its potential audience,

(i) senior undergraduate students and postgraduate students conducting research in the areas of CAD,

(ii) researchers at universities and other institutions working in these fields

and (iii) practitioners in the R&D departments of an organization working in these fields

This book differs from other books that also have CAD,

and CNC as the focus in two aspects

First of all,

integration is an essential theme of the book


STEP is used as a common data model for many integration implementations

The book can be used as an advanced reference for a course taught at the postgraduate level

It can also be used as a source of modern computer-aided technologies and contemporary applications in the areas of CAD,

since some 300 hundreds publications have been cited and listed in the reference lists of all chapters,

As the book title suggests,

the book commences with presentations of some of the basic principles (in Section I) and ends with integration implementations as well as implementation approaches (in Section II)

For readers who need a “crash course” or revision on topics of CAD,

in addition to integration issues,

both sections of the book can be found useful

Those who are well informed about these topics and only have an interest in integration issues can start with Section II,

or even better start with Chapter VII which discusses the integration issues based on feature concepts

Those who are conversant with CAD and CAM technologies but less acquainted with topics in CNC may skip the first 7 chapters

As mentioned above,

this book can also be used as an introduction to STEP data models,

Should this be of a reader’s interest,

the following chapters may be considered for study,

(a) Chapter II to read for some introduction to STEP and its use in exchanging CAD data

(b) Chapter XI to read for a grand idea of STEP-in,

STEP-out and STEP-throughout as in an integration implementation

(c) Chapter XIV to see how a STEP-based integration between machining and inspection may be achieved

and (d) Chapter XV to see how an Internet-based integration may be realized using STEP



(2005) The CAD/CAM Interface: A 25-year retrospective,

Transactions of ASME,

Journal of Computing and Information Science in Engineering,


Feature recognition by volume decomposition using halfspace partitioning

Advances in Design Automation,


DPP: An agent-based approach for distributed process planning

Journal of Intelligent Manufacturing,


Feature Recognition Methodologies and Beyond

Australian Journal of Mechanical Engineering,


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